Means and method of making geophysical explorations



June 27, w39- K. c. wooDYARD E-r AL" f y2,164,196

MEANS AND METHOD op MAKING GEoPmrsIcAL ExPLoRATroNs Filed March 31, 1934 Patented June 27, .1939 v MEANS aan Ms'rnon on Mciv enorm/stoer. nxrnoanrrons Kenneth o. Wosyani, wenn, La., ,Clifford a. Putnam, Kountze, Tex., and Harold R. Prescott, Ponca City, mda., assignors to Continental Gil Company, Ponca City,

Ation of Delaware ics kla., a corpora.-

appiieation Marca 31.1934. sei-iai No. hasta 6 Claims.

'One method of exploring subsurface forma.

tions consists in creating earth vibrations'by means of detonatng a charge of explosive or the like and recording the vibrations on suitable electrical apparatus. A seismophone, which is a form of microphone, picks up the earth vibrations and delivers them toianamplifying device-the output-of which. is used to operate a recording de- 15 vice, usually a photographic one. The conductors connecting the seismophone and the ampliner are usually of the same length and wound together into a cable. When these conductors -are near transmission lines, .telegraph A or telephone lines, or other sources of electrical energy, troublesome and undesirable voltages are induced in the conductors. Likewise, the motion' of the conductors through the earths magnetic field,

due to their movement as a result of -earth vibra- 25' tions, induces voltages in the conductors, which voltages interfere with the making of the exploration, as the results are obscured.

One object of our -invention is to provide a method of making. geophysical explorations in which -the effect* of extraneous voltages induced in the conductors connecting the seismophone to the amplier are annulled.

Another object of our invention is to provide a means for eliminating. the eiect of undesirable extraneous voltages induced in the conductors connecting the seismophone andthe amplier. f Further and other objects of our invention will lappear from the following description.

The accompanying drawing shows a schematic l'view of one device capable of carrying out the method of our invention and embodying the apparatus of our invention.`

. In general, our invention contemplates equalizing the impedances of the respective conductors i5 leading from the seismophone to the grid and to the cathode, so that the extraneousvoltages induced in the conductors will be of the same amplitilde and in the same phase.

` Mor'e particularly referring now to the drawfra'me 3,'to which is secured armature d, upon which are wound coils 5, connectedto conductors 'and'l. Conductors 6 and 'l lead to the grid 8 55V and cathode vil of an indirectly heated cathode to the cathode.

a seismophone I may consist of a resiliently ended magnet 2 provided with a 'housing or (cttw- 352) ltherxnionic tube ill. 'The conductors 6 and I may be of appreciable length inasmuch as the ampliiier unit may be at some disttmcefrom-thel seismophone I. The amplifier unit I I may con-- sist of the rst thermionic tube ID land a number of further amplifying tubes I2; Only one has'been shown in the drawing forpurposes of simplicity though it is to be understood that any number of amplifying stages Vmay be used as desired. 'I'he filament It of the tube I0 suppliesheat to. the -cathode 9 so that it acts as tron emission source. I il is connected to a positive terminal I6 of a plate battery I8.l Currentjfiows from the plate When the -grid potential of the an elec- The plate I of the tube tube changes with'respect to the cathode, a vari ation in plate current will occur. known to-those skilled in the art.

cathode and the grid were changed in potential the same amount with respect to the negative terminal of the plate Vbattery I8, no substantial change in plate current will take place. Due to the fact that the capacity to ground for the grid of the tube is less than the capacity to ground of the cathode if equal voltages were imposed upon conductors 8 and 'l in the arrangement shown, a variation in plate current would take place were it not for the balancer circuit of our invention. 'I'he balancer circuit consists of an impedance (shown as resistance I9) -which is connected across the conductors 6 and 'I andA 'Ihis .is well If 'both the connects the cathode' 9 and the grid 8. A definite potential' is impressed uponthe cathode 9 and thel grid ,8 by means of conductor 20, which is connected to the negative terminal of plate battery Il by meansl ofconductor 2|. "I'he conductor 2il terminates at an intermediate point in the 'resistance I9 so that the potential change of the grid caused by extraneous voltages is exactly equal to the potential changes of the cathode caused by the sameextraneous voltages. The

. balancer is operated by experimentally adjusting for minimum-disturbance by setting the arm at'- some point slightly different than the mid point to compensate for the difference between the impedance of the grid with respect to the earth and the cathode impedance with respect to the earth.

In eec't the impedance'of conductors v6 and I are able to b`e equalized by adjusting lthe point of contact of conductor20 to resistance I9.

The plate circuit of tube I Il has interposed therein the primary coil 23 of the transformer 24. The secondary coil 25 of the" transformer 24 is connected to grid 28 of tube I2. Filament 21 of tube I-2 is heated from llament battery 28.

7g ratus.

v aspring Il'whichmay be a hair spring or the like. The armature and its associated actuating magnet are housed in recorder housing 38. Within the recorder housing 1l! is positioned a secondary housing 40 containing an incandescent light 4| which is connected to a battery 42.

One wall of the housing 40 is provided with 'a lens 43 adapted to focus rays of light upon the mirror il. The reflected beam 44 from the mirror 3i falls upon a photographic nlm 45 which is moved by suitable actuating mechanism 40 driven by a motor 41 at a uniform speed.

In operation. a charge of explosive is detonated. This produces earth vibrations, which vibrations are picked lup by the frame 3 of the seismophone'. The magnet 2, due to its inertia, tends to remain stationary in space while the armature moves relativel thereto. secured to the frame I, a relative movement between the magnet 2 and the core 4 will take place.

'Ihe magnetic changes produced will induce voltages in coils 5 which are led by conductors 8 and 1 to the grid and cathode of tube I0. It will be noted that the arrangement is such that when conductor l is positive, conductor 1 will be negative, dueto the voltages induced in the coils 5. This will produce a chang'e in the relative potential between grid and cathode, causing a corresponding iluctuation in the plate current, as is well known in the art.

Conductors 6 and 1 are in the same cable and are closely associated thereby in a substantial fixed spatial relationship. Due to the fact that 4 the conductors are so closely placed, the same voltage will be induced in conductor B as in conductor 1 by an external magnetic field or by the movement of the conductors through the earths magnetic ileld. In other words, like voltages will 45 be induced in conductors 6 and 1 at any one' instant by reason of extraneous electrical disturbances.l

'I'he use of a balancer circuit enables us to cause these voltages to .be exactly equal. The

point of contact of balancer arm 20 may be adjusted to such a point on resistance I l that when the undesirable extraneous voltages are introyducedto grid 8 and cathode 9, the cathode and the grid will be aiiected to substantially the same 55 extent so that these voltages being of the same 44- Ato rise and fall in sympathy with the earthy tions near transmission lines and electrical equipment. Such explorations would be impossible without the use of our rnxethodl and appa- Inasmuch as core 4 is rigidly l arcaica A It will be seen, therefore, that we have 'accom--4 plished the objects of our invention.

Itwillbeunderstcodthatcertainfeaturesandsub-combinations are of utility and may be em,- 4.played without reference to other-.features and 'sub-combinations.' This is contemplated byand is within the scope of our claims. It is further obvious that various changes may be made in details within the scope of our claims without departing from the spirit of our invention. Por example, a variable impedance may be employed for resistance It. A capacity or an inductancc may be used 'to balance the inductance of the line, without departing from the scope of our invention. It is, therefore, to be understood that our invention is not to be limited to the specinc dey tails shown and described.

' Having thus described our invention, what we 1. Inan apparatus for making geophysical explorations, a seismophone, a thermionic tube having a grid and a cathode. a conductor connecting said grid and said seismophone, a coilductor connecting said cathode and said selsmo` phone, and means for equalizing the impedance of said conductors. y

2. In an apparatus for making geophysical explorations, a seismophone, a thermionic tube having a grid and-an indirectly heated cathode. a

conductor connecting said seismophone and said an grid, 'a conductor connecting said seismophone and said cathode and means for equalizing the impedance of said conductors whereby voltages vinduced in saidv conductors by an extraneous magnetic field will be of substantially the same amplitude and phase.

3. In an apparatus for making geophysical explorations, a thermionic tube having Aa grid and a cathode, a resistance connecting the grid and cathode and ymeans for impressing a negative lpotential at an intermediate point in said resistance the construction being such that the efi'ect of extraneous electrical disturbances is eliminated.

4. In an apparatus for making geophysical explorations, a thermionic tube having a grid and a cathode, an impedance connecting the grid and cathode and means for impressing a negative potential at an intermediate point in said impedance the construction being such that the effect of extraneous electrical disturbances is eliminated.

.5. In a seismograph system having a seismophone, a thermonic tube containing a grid, a

plate and a cathode, a source of plate potential for said tube, an amplification channel, a conductor connecting the seismophone to said grid, a conductor connecting said seismophone to said v cathode, means for impressing the output of said thermionic. tube upon said amplification channel. and means cpe'rated by the output of said amplication channel for recording voltage variations occurring in said seismophone, means 4for nullify.- l ing the eiIect of extraneously induced voltages in said conductors connecting the seismophone to' grid and cathode of said thermionic tube includ- -f ing in 'combination an impedance interposed between grid and cathode of said tube', said nnped. ance having a variable contact arm and means' electrically coupling said contact arm toanegative point of the source of' plate potential of said thermionic tube. l l v 6. In an apparatus for making geophysical explorations, a first thermionic tube having a grid and a cathode, a pair of conductors of considern arcaico 3 means for impressing the output of said first thermionic tube upon said amplication channel and recording means operated by the output of said amplification channel.

KENNETH C. WOODYARD. CLIFFORD A. PUTNAM. HAROLD R. PRESCO'II. 

